Constant voltage generating circuit

ABSTRACT

In a constant voltage generating circuit, a predetermined voltage outputted by voltage applying means connected between first and second power source terminals is simultaneously applied to the control electrode of a first MOS transistor of a first polarity and the control electrode of a second MOS transistor of a second polarity which are provided complementarily, and a voltage obtained by subtracting the threshold voltage of the first MOS transistor from the potential at the control electrode of the first MOS transistor is applied to the control electrode of a third MOS transistor of the second polarity while a voltage obtained by adding the potential at the control electrode of the second MOS transistor to the threshold voltage of the second MOS transistor is applied to a fourth MOS transistor of the first polarity, so that each of the third and fourth MOS transistors is operated in the critical state between the conductive state and the non-conductive state, whereby positive or negative noise voltage included in the output voltage of the circuit is quickly eliminated. 
     This is a Reissue of a Patent which was the subject of a Reexamination Certificate No. B1 4,670,706, dated Jul. 25, 1989, Request No. 90/001689.

BACKGROUND OF THE INVENTION

This invention relates to constant voltage generating circuits, and moreparticularly to a constant voltage generating circuit in the form of asemiconductor integrated circuit.

In the following description, insulated gate field-effect transistorswill be referred to as "MOS transistors", when applicable.

One example of a conventional constant voltage generating circuit is asshown in FIG. 5. In this circuit, a predetermined voltage is applied toa power source terminal 1, and a series circuit of a resistor 3 having aresistance R₃ and a resistor 4 having a resistance R₄ is connectedbetween the terminal 1 and ground. The connecting point 2 of theresistors 3 and 4 is an output terminal from which the output voltage ofthe constant voltage generating circuit is applied. A decouplingcapacitor 5 for stabilizing the output voltage at the output terminal 2is connected between the connecting point 2 and ground.

The operation of the conventional constant voltage generating circuitthus organized will now be described.

In the circuit of FIG. 5, the output voltage at the output terminal 2 isdetermined from the supply voltage at the power source terminal 1 andthe resistance of the resistors 3 and 4. That is, the output voltage V₂at the output terminal 2 is: ##EQU1## where V is the supply voltage atthe power source terminal 1.

As is apparent from equation (1), the output voltage V₂ changes inproportion to the supply voltage V. Therefore, the constant voltagegenerating circuit in FIG. 5 is employed as a voltage source where it isacceptable for the output voltage to follow the supply voltage, such asa reference voltage source in a sense amplifier circuit for a dynamicrandom access memory.

FIG. 6 shows another example of a conventional constant voltagegenerating circuit. In the circuit of FIG. 6, a predetermined voltage isapplied to a power source terminal 11, and a series circuit of aresistor 13 and a plurality of N-type MOS transistors 16a through 16n isconnected between the terminal 11 and ground. In each of the MOStransistors, the drain electrode is connected to the gate electrode.Each of the MOS transistors has a threshold voltage V_(THN). Theconnecting point 12 of the resistor 13 and the N-type MOS transistor16a, i.e, an output terminal, is grounded through a decoupling capacitor15 adapted to stabilize the output voltage of the output terminal 12.

The operation of the circuit shown in FIG 6 will be now described. Inthe case where the resistance of the resistor 13 is higher than theresistance of the N-type MOS transistors 16a through 16n which areturned on, then the output voltage V₁₂ at the output terminal 12 is:

    V.sub.12 ≈n·V.sub.THN                     ( 12)

Accordingly, the output V₁₂ is maintained constant irrespective of thevariation of the supply voltage at the power source terminal 11.Therefore, the constant voltage generating circuit in FIG 6 is employedas a voltage source in which the output voltage is independent of thesupply voltage, such as a reference voltage source for a MOS sidedifferential amplifier circuit in the transition from TTL level to MOSlevel.

In the circuit of FIG. 5, a DC current flows through the resistors 3 and4. In the circuit of FIG. 6, a DC current flows through the resistor 13and the N-type MOS transistors 16a through 16n. Therefore, it isnecessary to increase the resistance of the resistors 3, 4 and 13 asmuch as possible (several megohms to several tens of megohms) todecrease the DC currents as much as possible, to thereby minimize thepower consumption of the circuits. However, if the resistances areincreased, then the output voltage are liable to be affected by noisewhich is produced in the operation of the integrated circuit. Therefore,the output voltage must be stabilized by connecting a decouplingcapacitor (generally 10 pF to 100 pF) such as the capacitor 5 in FIG. 5or the capacitor 15 in FIG. 15. Such a decoupling capacitor occupies arelatively large part of the area of the semiconductor chip. This is oneof the difficulties accompanying the conventional constant voltagegenerating circuit.

In a dynamic random access memory to which the above-described constantvoltage generating circuits can be applied supply voltage variation iscommonly tested by repeatedly increasing and decreasing the supplyvoltage between 4.5 V and 5.5 V. In this connection, the conventionalconstant voltage generating circuits suffer from the difficulty that,because of the large resistance and the large stabilizing capacitance,the output voltage of the constant generating circuit cannot quicklyfollow the variation of the supply voltage; that is, it takes time forthe output voltage to reach the predetermined value, as a result ofwhich the time required for a supply voltage variation test isunavoidably long.

SUMMARY OF THE INVENTION

Accordingly, an object of this invention is to eliminate theabove-described difficulties accompanying a conventional constantvoltage generating circuit.

More specifically, an object of the invention is to provide a constantvoltage generating circuit in which a pair of MOS transistors arecomplementarily provided in the output stage thereof, and each of thesetransistors is operated in the critical state between the conductivestate and the nonconductive state thereof to quickly eliminated noisevoltage which may be included in the output voltage of the circuit,whereby the power consumption is reduced while the output voltage ismaintained free from noise voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood from the followingdescription in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of a first embodiment of a constantvoltage generating circuit according to the present invention;

FIG. 2 is a schematic diagram of a second embodiment of the constantvoltage generating circuit according to the present invention;

FIG. 3 is a schematic diagram of a third embodiment of the constantvoltage generating circuit according to the present invention;

FIG. 4 is a schematic diagram of a fourth embodiment of the constantvoltage generating circuit according to the present invention;

FIG. 5 is a schematic diagram of a constant voltage generating circuithaving an output voltage variable with supply voltage; and

FIG. 6 is a schematic diagram of a conventional constant voltagegenerating circuit having an output voltage independent of supplyvoltage.

DETAILED DESCRIPTION OF THE INVENTION

A first example of a constant voltage generating circuit according tothis invention is shown in FIG. 1. In this circuit, a predeterminedvoltage is applied to a first power source terminal 31. A series circuitof a resistor 33 having a resistance R₃₃ and a resistor 34 having aresistance R₃₄ is connected between the terminal 31 and ground. Theconnecting point 32 of the resistors 33 and 34 is connected to the gateelectrode of a P-type MOS transistor 35, the source electrode of whichis connected through a connecting point 36 and a resistor 37 to thefirst power source terminal 31. The drain electrode of the P-type MOStransistor 35 is grounded. The connecting point 32 is further connectedto the gate electrode of an N-type MOS transistor 38, the drainelectrode of which is connected to the first power source terminal. Thesource electrode of the transistor 38 is grounded through a connectingpoint 39 and a resistor 40. The connecting point 36 is connected to thegate electrode of an N-type MOS transistor 41, the drain electrode ofwhich is connected to the first power source terminal 31. The connectingpoint 39 is connected to the gate electrode of a P-type MOS transistor42, the drain electrode of which is grounded. The source electrodes ofthe N-type MOS transistor 41 and the P-type MOS transistor 42 areconnected together, thus providing an output terminal 43.

The operation of the circuit shown in FIG. 1 will now be described. Incircuit of FIG 1, the voltage at the connecting point 32 is determinedfrom the supply voltage at the terminal 31 and the resistances of theresistors 33 and 34. That is, the voltage V₃₂ at the connecting point 32can be represented by the following equation: ##EQU2## where V is thesupply voltage provided at the terminal 31.

The resistors 33 and 34 are electrically insulated from the outputterminal 43 and therefore not affected by the noise provided at theoutput terminal 43. Accordingly, the resistances of the resistors 33 and34 can be set to high values so that a DC current flowing through theresistors is decreased.

The resistance of the resistor 37 is set to more than 100 times theresistance of the P-type MOS transistor 35 provided when the latter 35is turned on. When, under this condition, the voltage V₃₂ at theconnecting point 32 is applied to the gate electrode of the MOStransistor 35, the voltage V₃₆ at the source electrode of the MOStransistor 35, i.e, at the connecting point 36, is:

    V.sub.36 =V.sub.32 +|V.sub.THP |         (4)

where V_(THP) is the threshold voltage of the P-type MOS transistor 35.

That is, voltage at the connecting point 36 is the sum of the gatepotential of the P-type MOS transistor 35 and its threshold voltage.

On the other hand, the resistance of the resistor 40 is set to more than100 times the resistance of the N-type MOS transistor 38 provided whenthe latter 38 is turned on. When, under this condition, the voltage V₃₂at the connecting point 32 is applied to the gate electrode of theN-type MOS transistor 38, the voltage at the source electrode of the MOStransistor 38, i.e., at the connecting point 39, is as follows:

    V.sub.39 =V.sub.32 -V.sub.THN                              (5)

where V_(THN) is the threshold voltage of the N-type MOS transistor 38.

That is, the voltage at the connecting point 39 is obtained bysubtracting the threshold voltage of the MOS transistor 38 from its gatepotential.

The voltage V₃₆ at the connecting point 36 is applied to the gateelectrode of the N-type MOS transistor 41, and the voltage V₃₉ at theconnecting point 39 is applied to the gate electrode of the P-type MOStransistor 42. For convenience in description, let it first be assumedthat the N-type MOS transistor 41 and the P-type MOS transistor 42 arenot connected to one another at the output terminal 43. In this case,the source potential V_(43') is lower by the threshold voltage than thegate potential V_(36') and therefore the source potential V_(43') is:##EQU3##

On the other hand, the P-type MOS transistor 42 is rendered conductiveonly when the source potential V_(43") becomes equal to or higher thanthe sum of the gate potential V₃₉ and the absolute value of thethreshold value.

Therefore, ##EQU4## From the equations (6) and (7), ##EQU5##

The equation (8) means that, even if the output terminal 43 isconnected, no current flows, and the voltage at the output terminal 43is maintained constant, V₃₂ +|V_(THP) |-V_(THN).

Under this condition, each of the MOS transistors 41 and 42 operates ina critical state between an "on" state and an "off" state. Therefore,for instance when a positive noise voltage is provided at the outputterminal 43, the P-type MOS transistor 42 is rendered conductive toeliminate the noise voltage. Similarly, when a negative noise voltage isprovided at the output terminal 43, the N-type MOS transistor 41 isrendered conductive to eliminate the noise voltage.

As is apparent from the equation (8), the output voltage at the outputterminal 43 is determined only by the voltage at the connecting point 32and the threshold voltages of the MOS transistors, and is completelyindependently of the resistances of the MOS transistors which areprovided when the latter are rendered conductive (on) (hereinafterreferred to as "on-resistances" when applicable).

Accordingly, the on-resistances of the MOS transistors 41 and 42 formingthe output stage of the constant voltage generating circuit can befreely decreased. Accordingly, in the case when the output voltage atthe output terminal 43 includes a noise voltage, the output impedance ofthe constant voltage generating circuit can be decreased, and thereforethe noise voltage can be eliminated quickly.

FIG. 2 shows a second example of the constant voltage generating circuitaccording to the invention. The circuit shown in FIG. 2 is equal to thatshown in FIG. 1 except for the following point. Instead of theresistance 34 in FIG. 1, a series circuit of an N-type MOS transistors44a through 44n are connected between the connecting point 32 andground. A circuit made up of the power source terminal 31, the resistor33, and the N-type MOS transistors 44a through 44n is equivalent to theconventional constant voltage generating circuit shown in FIG. 6. Aconstant voltage V₃₂ is provided at the connecting point 32 irrespectiveof the supply voltage at the power source terminal 31.

That is, if the resistance of the resistor 33 is set to about 100 timesthe on-resistance of the N-type MOS transistors 44a through 44n, thenthe voltage V₃₂ at the connecting point 32 is:

    V.sub.32≈n·V.sub.THN                      (9)

The operation of the circuit of FIG. 2 subsequent to the connectingpoint 32 is the same as that in FIG. 1. Therefore, the output voltageV₄₃ at the output terminal 43 can be represented by the followingequation (10):

    V.sub.43 =n·V.sub.THN +|V.sub.THP |-V.sub.THN

FIG. 3 shows a third example of the constant voltage generating circuitaccording to the invention. The circuit of FIG. 3 is similar to thecircuit shown in FIG. 1 except for the following point: In the firstexample shown in FIG. 1, each of the MOS transistors 41 and 42 operatesin the critical state between the "on" state and the "off" state.Therefore, in the case where, because of variations in manufacture, thethreshold voltages of the MOS transistors 41 and 42 are not equal tothose of the MOS transistors 35 and 38, both of the MOS transistors 41and 42 may be rendered conductive simultaneously, as a result of whichunwanted current may flow between the power source terminal 31 andground.

In order to overcome the difficulty, in the circuit of FIG. 3, aresistor 47 is connected between the resistors 33 and 34, and theconnecting points 45 and 46 are connected to the gate electrodes of theMOS transistors 35 and 38, respectively, so that a potential differencecorresponding to a voltage drop across the resistor 47 is providedbetween the gates of the MOS transistors. Accordingly, in the circuit ofthe FIG. 3, the P-type MOS transistor 42 operates in the "off" regionaccording to the voltage drop by the resistor 47, which compensates forthe variations in threshold voltage of the MOS transistors which may becaused during manufacture.

FIG. 4 shows a fourth example of the constant voltage generatingcircuit. The circuit of FIG. 4 is similar to that of FIG. 1 except forthe following point: In the circuit of FIG. 4, high resistance MOStransistors 33', 34', 37' and 40' are employed instead of the resistors33, 34, 37 and 40 in FIG. 1 because a MOS transistor resistance elementis higher in resistance and smaller in occupied area than a diffusionlayer or polysilicon resistance element

As is apparent from the above description, according to the invention,the complementarily coupled MOS transistors are provided in the outputstage of the constant voltage generating circuit, and each of the MOStransistor is operated in the critical state between the "on" state andthe "off" state. Therefore, positive or negative noise voltages includedin the output voltage can be quickly suppressed. Furthermore, when nonoise is included in the output voltage, current scarcely flows betweenthe power source terminal and the ground, and therefore the powerconsumption is decreased as much. In addition, since no capacitor forstabilizing the output voltage is required, the tracking characteristicof the output voltage with respect to the supply voltage variation canbe improved, and the time required for a supply voltage variation testor the like can be shortened.

What is claimed is: .[.
 1. A constant voltage generating circuitcomprising:a first insulated gate field-effect transistor of a firstpolarity having a pair of main electrodes and a control electrode andconnected between a first power source terminal and an output terminal;a second insulated gate field-effect transistor of a second polarityhaving a pair of main electrodes and a control electrode and connectedbetween said output terminal and a second power source terminal; andcontrol voltage applying means for applying a first intermediatepotential provided between a first potential at said first power sourceterminal and a second potential at said second power source terminal tothe control electrode of said first insulated gate field-effecttransistor, and for applying a second intermediate potential providedbetween said first potential and said second potential to the controlelectrode of said second insulated gate field-effect transistor, saidfirst intermediate potential being at all times greater than said secondintermediate potential by substantially the sum of the thresholdvoltages of said first and second insulated gate field-effecttransistors..].
 2. A constant voltage generating circuit comprising:afirst insulated gate field-effect transistor of a first polarity havinga pair of main electrodes and a control electrode and connected betweena first power source terminal and an output terminal; a second controlinsulated gate field-effect transistor of a second polarity having apair of main electrodes and a control electrode and connected betweensaid output terminal and a second power source terminal; control voltagegenerating means for applying a first intermediate potential providedbetween a first potential at said first power source terminal and asecond potential at said second power source terminal to the controlelectrode of said first insulated gate field effect transistor, and forapplying a second intermediate potential provided between said firstpotential and said second potential to the control electrode of saidsecond insulated gate field-effect transistor, said first intermediatepotential being at all times greater than said second intermediatepotential by substantially the sum of threshold voltages of said firstand second insulated gate field-effect transistors, said control voltagegenerating means comprising: voltage division potential means connectedbetween said first and second power source terminals, for providing avoltage division potential at an output node; first control voltagegenerating means having a third insulated gate field-effect transistorof said second polarity, said third insulated gate field-effecttransistor having a pair of main electrodes and a control electrode, oneof said pair of main electrodes being connected to said first powersource terminal through a first load element and to the controlelectrode of said first insulated gate field-effect transistor, theother main electrode being connected to said second power sourceterminal, and said control electrode being connected to said output nodeof said voltage division potential generating means, for providing saidfirst intermediate potential at said one main electrode; and secondcontrol voltage generating means having a fourth insulated gatefield-effect transistor of said first polarity; said fourth insulatedgate field-effect transistor having a pair of main electrodes and acontrol electrode, one of said main electrodes being connected to saidsecond power source terminal through a second load element and to thecontrol electrode of said second insulated gate field-effect transistor,the other main electrode being connected to said first power sourceterminal, and said control electrode being connected to said output nodeof said voltage division potential generating means, for providing saidsecond intermediate potential at said one main electrode of said fourthinsulated gate field-effect transistor.
 3. A constant voltage generatingcircuit as claimed in claim 2, in which said first intermediatepotential provided by said first control voltage generating means is thesum of said voltage division potential and the threshold voltage of saidthird insulated gate field-effect transistor, and said secondintermediate potential provided by said second control voltagegenerating means is the difference obtained by subtracting the thresholdvoltage of said fourth insulated gate field-effect transistor from saidvoltage division potential.
 4. A constant voltage generating circuit asclaimed in claim 2, in which said first load element in said firstcontrol voltage generating means is a fifth insulated gate field-effecttransistor of said first polarity, and said second load element in saidsecond control voltage generating means is a sixth insulated gatefield-effect transistor of said second polarity.
 5. A constant voltagegenerating circuit as claimed in claim 2, in which:said voltage divisionpotential generating means has a seventh insulated gate field-effecttransistor of said first polarity connected between said first powersource terminal and said output node, and an eighth insulated gatefield-effect transistor of said second polarity connected between saidoutput node and said second power source terminal, and said first loadelement in said first control voltage generating means is a fifthinsulated gate field-effect transistor of said first polarity, and saidsecond load element in said second control voltage generating means is asixth insulated gate field-effect transistor of said second polarity. 6.A constant voltage generating circuit as claimed in claim 19, in whichsaid control voltage applying means comprises:voltage division potentialgenerating means having first and second output nodes, a first resistiveelement connected between said first power source terminal and saidfirst output node, a second resistive element connected between saidfirst and second output nodes, and a third resistive element connectedbetween said second output node and said second power source terminal;first control voltage generating means comprising a third insulated gatefield-effect transistor of said second polarity having a pair of mainelectrodes and a control electrode, one of said main electrodes beingconnected to said first power source terminal through a first loadelement and to the control electrode of said first insulated gatefield-effect transistor, the other main electrode being connected tosaid second power source terminal, and said control electrode being saidsecond output node of said voltage division potential generating means,for providing said first intermediate potential at said one mainelectrode of said third insulated gate field effect transistor; andsecond control voltage generating means comprising a fourth insulatedgate field-effect transistor of said first polarity having a pair ofmain electrodes and a control electrode, one of said main electrodesbeing connected to said second power source terminal through a secondload element, the other main electrode being connected to said firstpower source terminal, and said control electrode being connected tofirst output node of said voltage division potential generating means,for providing said second intermediate potential at said one mainelectrode of said fourth insulated gate field-effect transistor.
 7. Aconstant voltage generating circuit, comprising:a first insulated gatefield-effect transistor having a pair of main electrodes and a controlelectrode and connected between a first power source terminal and anoutput terminal; a second insulated gate field-effect transistor havinga pair of main electrodes and a control electrode and connected betweensaid output terminal and a second power source terminal; voltagedivision potential generating means connected between said first andsecond power source terminals, for providing a voltage divisionpotential at an output node thereof; a third insulated gate field-effecttransistor of said second polarity having a pair of main electrodes anda control electrode, one of said main electrodes being connected to saidfirst power source terminal through a first load element and to thecontrol electrode of said first insulation gate field-effect transistor,the other main electrode being connected to said second power sourceterminal, and said control electrode being connected to said output nodeof said voltage division potential generating means; and a fourthinsulated gate field-effect transistor of said first polarity having apair of main electrodes and a control electrode, one of said mainelectrodes being connecting to said second power source terminal througha second load element and to the control electrode of said secondinsulated gate field-effect transistor, the other main electrode beingconnected to said first power source terminal, and said controlelectrode being connected to said output node of said voltage divisionpotential generating means.
 8. A constant voltage generating circuit asclaimed in claim 7, in which each of said first and second insulatedgate field-effect transistors operates in the critical state between theconductive state and the non-conductive state thereof.
 9. A constantvoltage generating circuit as claimed in claim 7, which said voltagedivision potential generating means comprises: a first resistive elementconnected between said first power source terminal and said output node;and a second resistive element connected between said second powersource terminal and said output node.
 10. A constant voltage generatingcircuit as claimed in claim 9, in which said second resistive element isa series circuit of a plurality of insulated gate field-effecttransistors.
 11. A constant voltage generating circuit as claimed inclaim 9, in which said first resistive element is a seventh insulatedgate field-effect transistor of said first polarity, and said secondresistive element is an eighth insulated gate field-effect transistor ofsaid second polarity.
 12. A constant voltage generating circuit asclaimed in claim 7, in which said first load element is a fifthinsulated gate field-effect transistor of said first polarity, and saidsecond load element is a sixth insulated gate field-effect transistor ofsaid second polarity, and said voltage division potential generatingmeans comprises: a seventh insulated gate field-effect transistor ofsaid first polarity connected between said first power source terminaland said output node; and an eighth insulated gate field-effecttransistor of said second polarity connected between said output nodeand said second power source terminal.
 13. A constant voltage generatingcircuit, comprising:a first insulated gate field-effect transistor of afirst polarity having a pair of main electrodes and a control electrode,said first insulated gate field-effect transistor being connectedbetween a first power source terminal and an output terminal; a secondinsulated gate field-effect transistor of a second polarity having apair of main electrodes and a control electrode and connected betweensaid output terminal and a second power source terminal; voltagedivision potential generating means connected between said first powersource terminal and said second power source terminal and having firstand second nodes, for providing first and second voltage divisionpotentials respectively at said first and second nodes, said firstvoltage division potential being higher than said second voltagedivision potential; a third insulated gate field-effect transistor ofsaid second polarity having a pair of main electrodes and a controlelectrode, one of said main electrodes being connected to said firstpower source terminal through a first load element and to the controlelectrode of said first insulated gate field-effect transistor, theother main electrode being connected to said second power sourceterminal, and said control electrode being connected to said secondoutput node of said voltage division potential generating means; and afourth insulated gate field-effect transistor of said first polarityhaving a pair of main electrodes and a control electrode, one of saidmain electrodes being connected to said second power source terminalthrough a second load element and to the control electrode of saidsecond insulated gate field-effect transistor, the other main electrodebeing connected to said first power source terminal, and said controlelectrode being connected to said first output node of said voltagedivision potential generating means.
 14. A constant voltage generatingcircuit as claimed in claim 11, in which said voltage division potentialgenerating means comprises: a first resistive element connected betweensaid first power source terminal and said first output node; a secondresistive element connected between said first and second output nodes;and a third resistive element connected between said second output nodeand said second power source terminal.
 15. A constant voltage generatingcircuit as claimed in claim 12, in which each of said first and secondinsulated gate field-effect transistor operates in the critical statebetween the conductive state and the non-conductive state thereof..[.16. A constant voltage generating circuit, comprising:a first outputtransistor of a first polarity and having its conduction path coupledbetween a first source potential and an output terminal; a second outputtransistor of a second polarity and having its conduction path coupledbetween said output terminal and a second source potential; each of saidfirst and second output transistors having a control electrode andhaving a conductive state, a non-conductive state and a critical rangebetween the conductive and non-conductive states where the potentialdifference between its control electrode and output terminal issubstantially equal to the threshold voltage of the transistor; andcontrol means for providing control voltages to control electrodes ofsaid first and second output transistors to simultaneously operate bothof said output transistors in said critical range between their off andon states..]. .[.17. A constant voltage generating circuit, comprising:a first insulated gate field-effect transistor of a first polarityhaving a pair of main electrodes and a control electrode and connectedbetween a first power source terminal and an output terminal; a secondinsulated gate field-effect transistor of a second polarity having apair of main electrodes and a control electrode and connected betweensaid output terminal and a second power source terminal; and controlvoltage applying means for applying a first intermediate potentialprovided between a first potential at said first power source terminaland a second potential at said second power source terminal to thecontrol electrode of said first insulated gate field-effect transistor,and for applying a second intermediate potential provided between saidfirst potential and said second potential to the control electrode ofsaid second insulated gate field-effect transistor, said first andsecond intermediate potentials changing in response to changes in saidfirst and second potentials to change the conductivities of said firstand second output transistors and maintain a constant voltage at saidoutput terminal despite fluctuations in said first or secondpotentials..].
 18. A constant voltage generating circuit, comprising:afirst insulated gate field-effect transistor of a first polarity havinga pair of main electrodes and a control electrode and connected betweena first power source terminal and an output terminal; a second insulatedgate field-effect transistor of a second polarity having a pair of mainelectrodes and a control electrode and connected between said outputterminal and a second power source terminal; control voltage applyingmeans for applying a first intermediate potential provided between afirst potential at said first power source terminal and a secondpotential at said second power source terminal to the control electrodeof said first insulated gate field-effect transistor, and for applying asecond intermediate potential provided between said first potential andsaid second potential to the control electrode of said second insulatedgate field effect transistor, said first intermediate potential being atall times greater than said second intermediate potential bysubstantially the sum of the threshold voltage of the said first andsecond insulated gate field effect transistors, said first and secondintermediate potential applying means comprising transistors of saidsecond and first polarities, respectively.
 19. A constant voltagegenerating circuit comprising:a first insulated gate field-effecttransistor of a first polarity having a pair of main electrodes and acontrol electrode and connected between a first power source terminaland an output terminal; a second control insulated gate field-effecttransistor of a second polarity having a pair of main electrodes and acontrol electrode and connected between said output terminal and asecond power source terminal; and control voltage applying means forapplying a first intermediate potential provided between a firstpotential at said first power source terminal and a second potential atsaid second power source terminal to the control electrode of said firstinsulated gate field effect transistors, and for applying a secondintermediate potential provided between said first potential and saidsecond potential to the control electrode of said second insulated gagefield-effect transistor, said first intermediate potential being at alltimes greater than said second intermediate potential by substantiallythe sum of the absolute value of the threshold voltage of said firstinsulated gate field-effect transistor and the threshold voltage of saidsecond insulated gate field effect transistor minus a predeterminedvoltage, said first and second intermediate potential applying meanscomprising transistors of said second and first polarities,respectively..]. .Iadd.20. A constant voltage generating circuit,comprising:a first output transistor of a first polarity and having itsconduction path coupled between a first power source terminal and anoutput terminal; a second output terminal of a second polarity andhaving its conduction path coupled between said output terminal and asecond power source terminal; each of said first and second outputtransistors having a control electrode and having a conductive state, anon-conductive state and a critical range between the conductive andnon-conductive states where the potential difference between its controlelectrode and output terminal is substantially equal to the thresholdvoltage of the transistor; and control means for providing controlvoltages to control electrodes of said first and second outputtransistors to simultaneously operate both of said transistors in saidcritical range between their off and on states and such that said firstoutput transistor conducts if a negative noise voltage occurs at saidoutput terminal and said second output transistor conducts if a positivenoise voltage occurs at said output terminal. .Iaddend. .Iadd.21. Theconstant voltage generating circuit of claim 20, wherein said controlvoltage providing means comprises means for generating a predeterminedvoltage which is independent of a potential difference between saidfirst and second power source terminals..Iaddend. .Iadd.22. The constantvoltage generating circuit of claim 20, wherein said second controlvoltage has a value such that said second output transistor is operatedin said non-conductive state..Iaddend. .Iadd.23. The constant voltagegenerating circuit of claim 20, wherein said second control voltage hasa value such that said second output transistor is operated in saidnon-conductive state to compensate for variations in threshold voltagesof said first and second outupt transistors..Iaddend.